1. Field of the Invention
The present invention generally relates to oil and gas production operations, and more particularly to gas-lift plunger devices for lifting production fluids to the surface to restore production to shut in wells.
2. Description of the Prior Art
Gas lift plunger apparatus has been in use for many decades and has a long history of development. In one recent example, U.S. Pat. No. 7,438,125, Victor, a bypass assembly of a plunger lift device employs a bypass valve assembly having both an internal cage and an outer cage. The internal cage, when rotated using an adjustment performed with tools at the surface, operates to vary the size of the bypass orifices of the bypass valve and thus vary the bypass fluid volume. In addition a clutch within the lower part of the outer cage is used to maintain the valve push rod in a fixed position within the valve assembly until the push rod is forced to change the valve from an open (bypass) configuration to a closed (no bypass) configuration. The clutch tension is provided by a plurality of small metal coil springs wrapped around the clutch bobbin that surrounds the push rod. Some disadvantages of this design are its complexity that increases its cost and the effects of corrosion which predisposes the clutch assembly to premature failure. Another drawback is that the bypass orifices are cut at right angles through the inner and outer cages, which impedes the flow of fluid through the plunger as it descends through the tubing.
In another example, U.S. Patent Application Publication No. 2010/0294507, Tanton (See also U.S. Pat. No. 6,467,541, Wells) discloses two different free piston embodiments in which one or both of their components are made of materials that are at least partly buoyant. One embodiment is a simple combination of a sleeve having a seat to receive a ball at its lower end, as in a ball-check valve. In operation the ball is allowed to fall through the fluid in the well bore, followed by the sleeve at some time interval. The ball reaches the bottom of the well first. When the sleeve arrives it contacts the ball, which seals the well bore. Gas pressure can then lift the ball and sleeve together to the surface, pushing the production fluid ahead of them upward through the well bore. The other embodiment eliminates the separate ball or plug and closes the lower end of the sleeve, thus presenting a closed face to whatever material is in the well casing during descent. While simple in configuration, the first lacks predictability because the sleeve and ball operate independently until they reach the bottom of the well bore, and the second lacks broad utility because of its buoyancy and is not able to bypass fluids as it descends to the bottom of the well. Variations in the ball-check valve concept have been in the art for decades, as for example is illustrated in U.S. Pat. No. 2,001,012 patented May 14, 1935.
What is needed is an improved plunger bypass valve mechanism for a gas lift plunger device that is simple and durable, as well as reliable in operation and low in cost to manufacture.